A team of Japanese scientists has managed to turn mouse stem cells into viable eggs—that can be inseminated and go on to produce normal, healthy mouse pups. The finding has massive implications for the development of infertility treatments in the future.

The team of researchers from Kyoto University has previously created fully grown adult mice using sperm created from stem cells—but that's comparatively straightforward. Sperm, you see, are some of the simpler cells in the body: eggs are far more complex.

In this new study, published in Science, the researchers took embryonic stem cells, and induced pluripotent stem cells (iPSCs) from them. They then used a host of signaling molecules to slowly transform the iPSCs into egg precursors known as primordial germ cells. After further coddling in lab-grown ovary tissue, the cells—over the course of four weeks—matured into eggs.

The scientists fertilized these eggs and transplanted the resulting embryos in to foster mothers. A short while later, healthy offspring emerged, which went on to become fertile themselves. All in, it's a long and involved process—but, amazingly, it works.

The finding gives a useful glimpse into the processes at play during meiosis, the cell-division process which is peculiar to sex cells like eggs. But perhaps more interesting are the possibilities for the development of new infertility treatments in the future.

As ever, just because something's possible in a mouse doesn't mean it will necessarily work in a human model, but that won't stop the team trying: indeed, they're already starting to work with human stem cells instead. Expect a wait before you hear of this kind of technology being used in a clinical, as opposed to research, setting, though, because the ethical issues surrounding it will be close to impossible to settle. [Science via Nature]